Emails from one domain not getting to every account on server

I'm using cPanel 11 and I am having a problem with emails being sent to one pesky email account. I am running Spam Assassin and have a filter set to automatically delete all emails with a spam score above 5.0. I do not have any other filters currently running.

The emails are coming from Constant Contact (email marketing company) and every account on my server receives it fine except for a new webmaster@ account that I just set up which almost never receives the emails from CC's domains. If I send the offending email to my personal account (another ISP) or from one of the accounts on my server that IS accepting email correctly and then forward it to the webmaster@ account it gets there without a problem.

I've been getting other emails just fine on that account and *some* emails from Constant Contact, but not all. I got a list of their domains and about 15 IPs they share and I whitelisted them everywhere I could think of - SpamAssassin, email whitelists, and checked for blocked IPs in the IP Deny Manager. Still no emails. I even went so far as to turn off every filter and Spam Assassin to see if they were the culprit - still no emails from that domain getting to that address. The addresses that are getting the email report a "X-Spam-Status: No, score=-2.4" so it's not spam.

I'm thinking I overlooked something when I set up the initial webmaster@ account but I can't figure it out. Any suggestions would be greatly appreciated! Thank you.